Hot summers with high humidity. Mild winters requiring some heating. Climate zone 2A covers parts of Louisiana, Mississippi, Alabama, Georgia, Texas, Florida, including cities like Houston, New Orleans, Mobile, Savannah, Jacksonville. Cooling runs most of the year and your AC capacity is the main sizing decision. Heating is a secondary concern in zone 2A.
Climate zone 2A is the upper Gulf Coast: Houston, New Orleans, Mobile, and most of central Florida. Summers hit 95°F with 80 percent humidity, and the cooling season runs nine months. The defining HVAC challenges here are the long cooling season, flood-prone equipment placement, and the latent (dehumidification) load that single-stage equipment struggles to handle.
Why Flood Zone Equipment Placement Matters
Houston, New Orleans, and Mobile all sit on flat coastal plain with high water tables and a long history of hurricane and flood events. Hurricane Harvey (2017) flooded an estimated 200,000 Houston homes, and a meaningful share of those replaced their HVAC equipment afterward. The pattern after Harvey changed how new installs get specified: outdoor condensers move to elevated platforms 18 to 24 inches above the FEMA base flood elevation, and indoor air handlers move from ground-floor closets and garages into attic spaces or upper floors.
The elevated condenser pad adds $400 to $900 to install cost vs a slab on grade. The attic air handler swap on a retrofit adds $1,500 to $3,500 because of new return duct routing. CenterPoint Energy's SCORE program rebate ($600 to $1,800 for qualifying heat pumps) helps offset the cost.
Sizing for Humid Heat: Why Smaller Often Wins
Houston's 80 percent summer humidity makes dehumidification 40 to 50 percent of total cooling work. An oversized AC short-cycles, satisfies the thermostat in 6 to 8 minutes, then shuts off. The house ends up cool and clammy at 72°F and 65 percent humidity. Comfort suffers, mold risk climbs, and the AC actually runs less efficiently because it never reaches steady state.
A correctly-sized variable-speed heat pump runs at 30 to 60 percent capacity for hours at a time, holds the coil at saturation temperature, and pulls moisture out continuously. Indoor humidity stays below 55 percent without a separate dehumidifier. The same house with an oversized single-stage AC needs a $1,500 to $2,500 dehumidifier added later to fix the comfort problem.
Typical Houston HVAC Replacement Costs and Annual Operating
Houston HVAC replacement costs run $7,000 to $12,000 for a complete heat-pump or AC-plus-furnace install on a typical 2,000 square foot home. Annual heating and cooling cost varies sharply by system type and grid pricing.
| System type | Install cost | Annual operating (2,000 sq ft) |
|---|---|---|
| Traditional AC + 95% gas furnace | $7,500 to $10,500 | $1,400 to $1,800 |
| Heat pump with electric resistance backup | $6,500 to $9,500 | $1,300 to $1,900 |
| Heat pump with gas furnace backup (dual fuel) | $9,000 to $12,500 | $1,100 to $1,500 |
| Variable-speed heat pump only | $8,500 to $13,000 | $1,200 to $1,700 |
Design Temperatures for Zone 2A
Design temperatures are the outdoor conditions your HVAC system needs to handle. Winter design temp is the temperature your house must stay warm at. Summer design temp is the temperature your house must stay cool at. Use these as Manual J inputs.
| Condition | Range | What it means for sizing |
|---|---|---|
| Winter design temp | 15°F to 35°F | Heating equipment must hold setpoint at this outdoor temp. |
| Summer design temp | 90°F to 98°F | Cooling equipment must hold setpoint at this outdoor temp. |
| Heating degree days | 1,500 to 3,000 | Higher numbers mean longer, colder winters and more heating runtime. |
| Cooling degree days | 2,500 to 4,000 | Higher numbers mean longer, hotter summers and more AC runtime. |
| Load priority | Cooling dominated | Cooling runs most of the year and your AC capacity is the main sizing decision. Heating is a secondary concern in zone 2A. |
Cities in Climate Zone 2A
These US cities are typically classified as climate zone 2A. Zone boundaries follow county lines, so suburbs of these cities sometimes fall into adjacent zones.
| City | Climate type | HVAC priority |
|---|---|---|
| Houston | Hot, moist | High cooling loads with humidity control |
| New Orleans | Hot, moist | High cooling loads with humidity control |
| Mobile | Hot, moist | High cooling loads with humidity control |
| Savannah | Hot, moist | High cooling loads with humidity control |
| Jacksonville | Hot, moist | High cooling loads with humidity control |
Insulation Requirements for Zone 2A
IECC code sets minimum insulation R-values by climate zone. These are the numbers your local building inspector checks during framing. Better envelope insulation lowers your HVAC load and lets you install smaller equipment.
| Assembly | Required R-value | Where it goes |
|---|---|---|
| Walls (above grade) | R-13 to R-15 | Between studs, often with continuous foam outside the sheathing |
| Ceiling / attic | R-30 to R-38 | Loose-fill or batts on the attic floor, or spray foam on the roof deck |
| Floor / crawlspace | R-13 to R-19 | Between floor joists, or on crawlspace walls if conditioned |
For a state-by-state breakdown of insulation requirements, see our insulation R-values guide.
HVAC Equipment Requirements for Zone 2A
These are the system types that fit zone 2A conditions. Final selection depends on your fuel cost, your building envelope, and the actual Manual J load for your specific house.
| Equipment | Why it fits zone 2A |
|---|---|
| Heat pumps with backup heat | High cooling loads with humidity control |
| High-efficiency AC with dehumidification | Moderate heating requirements |
| Dual-fuel systems | Mold and moisture management |
| Whole-house dehumidifiers | Hurricane considerations in coastal areas |
Key HVAC Design Considerations in Zone 2A
These are the design issues that come up most in climate zone 2A:
- High cooling loads with humidity control
- Moderate heating requirements
- Mold and moisture management
- Hurricane considerations in coastal areas
- Year-round humidity concerns
Energy Code Rules for Zone 2A
Most states in zone 2A have adopted the IECC for residential construction. Equipment efficiency rules typically include:
- SEER 13+ minimum
- HSPF 7.7+ for heat pumps
- Moisture control strategies
- Duct leakage testing
Check your state's adopted code edition (some states are still on IECC 2018, others have moved to IECC 2021 or 2024). For the full state breakdown, see our HVAC building code requirements guide.
States with Zone 2A Areas
These states have counties classified as climate zone 2A. Not every county in these states is zone 2A, so check the IECC map for your specific county.
Frequently Asked Questions
What does IECC climate zone 2A mean?
Climate zone 2A is hot and moist. Hot summers with high humidity. Mild winters requiring some heating.
What are the design temperatures for climate zone 2A?
In climate zone 2A, the summer design temperature runs 90°F to 98°F and the winter design temperature runs 15°F to 35°F. These are the outdoor temperatures your HVAC system needs to handle without falling behind on the hottest summer day and coldest winter day.
Is climate zone 2A heating or cooling dominated?
Climate zone 2A is generally cooling dominated. Heating degree days run 1,500 to 3,000. Cooling degree days run 2,500 to 4,000. Cooling runs most of the year and your AC capacity is the main sizing decision. Heating is a secondary concern in zone 2A.
Which cities are in climate zone 2A?
Major US cities in IECC climate zone 2A include Houston, New Orleans, Mobile, Savannah, Jacksonville. Zone boundaries follow county lines, so check the IECC map for your exact county if you're outside these cities.
What insulation does climate zone 2A require?
IECC code-required insulation for climate zone 2A: walls R-13 to R-15, ceiling R-30 to R-38, floor R-13 to R-19. These are minimum R-values for new construction and major renovations. Higher R-values lower your HVAC load and let you use smaller equipment.
What HVAC equipment works best in climate zone 2A?
Common equipment choices for climate zone 2A include Heat pumps with backup heat, High-efficiency AC with dehumidification, Dual-fuel systems, Whole-house dehumidifiers. Final selection depends on your building envelope, fuel availability, electric rates, and the actual Manual J load calculation for your home.
How do I size HVAC for climate zone 2A?
Use the climate zone 2A design temperatures (winter 15°F to 35°F, summer 90°F to 98°F) as the outdoor design conditions in a Manual J load calculation. Our free residential load calculator plugs these in automatically when you select your city.
What energy code applies in climate zone 2A?
Most states in climate zone 2A have adopted some version of the IECC (International Energy Conservation Code) for residential construction. Equipment efficiency rules apply: SEER 13+ minimum. HSPF 7.7+ for heat pumps. Moisture control strategies. Duct leakage testing.